The concurrent validity of the Hamilton Rating Scale for Depression (HAMD-17) and the Montgomery-Åsberg Depression Rating Scale (MADRS) against the DSM-IV diagnosis ‘depressive disorder’ was assessed in patients with Parkinson's disease (PD). Sixty-three non-demented Parkinson's Disease (PD) patients who attended the outpatient department of an academic hospital were diagnosed according to a standardised research protocol. This protocol consisted of the Schedules for Clinical Assessment in Neuropsychiatry (SCAN) to establish the presence or absence of ‘depressive disorder’ according to the DSM-IV criteria, as well as the HAMD-17 and the MADRS. Receiver Operating Characteristics curves (ROC curves) were obtained and the positive and negative predictive values (PPV, NPV) were calculated for different cut-off scores. Maximum discrimination between depressed and non-depressed patients was reached at a cut-off score of 13/14 for the HAMD-17, and at 14/15 for the MADRS. At lower cut-offs, like 11/12 for the HAMD-17 and 14/15 for the MADRS, the high sensitivity and NPV make these scales good screening instruments. At higher cut-offs, such as 16/17 for the HAMD-17 and 17/18 for the MADRS, the high specificity and PPV make these instruments good diagnostic instruments. The diagnostics performance of the HAMD-17 is slightly better than that of the MADRS. This study shows that it is justified to use the HAMD-17 and the MADRS to measure depressive symptoms in both non-depressed and depressed PD patients, to diagnose depressive disorder in PD, and to dichotomize patient samples into depressed and non-depressed groups. Copyright © 2000 John Wiley & Sons, Ltd.